arXiv subjects

Natalie B. Hogg

Publications and source records attributed to Natalie B. Hogg.

22 records · Page 2Linked to original sources

arXiv2021

Strongly lensed supernovae as a self-sufficient probe of the distance duality relation

The observation of strongly lensed Type Ia supernovae enables both the luminosity and angular diameter distance to a source to be measured simultaneously using a single observation. This feature can be used to measure the distance duality parameter $η(z)$ without relying on multiple datasets and cosmological assumptions to reconstruct the relation between angular and luminosity distances. In this paper, we show how this can be achieved by future observations of strongly lensed Type Ia systems. Using simulated datasets, we reconstruct the function $η(z)$ using both parametric and non-parametric approaches, focusing on Genetic Algorithms and Gaussian processes for the latter. In the parametric approach, we find that in the realistic scenario of $N_{\rm lens}=20$ observed systems, the parameter $ε_0$ used to describe the trend of $η(z)$ can be constrained with the precision achieved by current SNIa and BAO surveys, while in the futuristic case ($N_{\rm lens}=1000$) these observations could be competitive with the forecast precision of upcoming LSS and SN surveys. Using the machine learning approaches of Genetic Algorithms and Gaussian processes, we find that both reconstruction methods are generally well able to correctly recover the underlying fiducial model in the mock data, even in the realistic case of $N_{\rm lens}=20$. Both approaches learn effectively from the features of the mock data points, yielding $1σ$ constraints that are in excellent agreement with the parameterised results.

astro-ph.CO↗

arXiv2020

Constraints on the distance duality relation with standard sirens

We use gravitational wave (GW) standard sirens, in addition to Type Ia supernovae (SNIa) and baryon acoustic oscillation (BAO) mock data, to forecast constraints on the electromagnetic and gravitational distance duality relations (DDR). We make use of a parameterised approach based on a specific DDR violation model, along with a machine learning reconstruction method based on the Genetic Algorithms. We find that GW provide an alternative to the use of BAO data to constrain violations of the DDR, reaching $3\%$ constraints on the violation parameter we consider when combined with SNIa, which is only improved by a factor of $\approx1.4$ if one instead considers the combination of BAO and SNIa. We also investigate the possibility that a neglected modification of gravity might lead to a false detection of DDR violations, even when screening mechanisms are active. We find that such a false detection can be extremely significant, up to $\approx10σ$ for very extreme modified gravity scenarios, while this reduces to $\approx4σ$ in a more realistic case. False detections can also provide a smoking gun for the modified gravity mechanism at play, as a result of the tension introduced between the SNIa+GW and SNIa+BAO combinations.

astro-ph.CO↗

arXiv2020

Latest evidence for a late time vacuum -- geodesic CDM interaction

We perform a reconstruction of the coupling function between vacuum energy and geodesic cold dark matter using the latest observational data. We bin the interaction in seventeen redshift bins but use a correlation prior to prevent rapid, unphysical oscillations in the coupling function. This prior also serves to eliminate any dependence of the reconstruction on the binning method. We use two different forms of the correlation prior, finding that both give similar results for the reconstruction of the dark matter -- dark energy interaction. Calculating the Bayes factor for each case, we find no meaningful evidence for deviation from the null interacting case, i.e. $Λ$CDM, in our reconstruction.

astro-ph.CO↗

arXiv2019

Constraints on the interacting vacuum -- geodesic CDM scenario

We investigate an interacting dark sector scenario in which the vacuum energy is free to interact with cold dark matter (CDM), which itself is assumed to cluster under the sole action of gravity, i.e. it is in free fall (geodesic), as in $Λ$CDM. The interaction is characterised by a dimensionless coupling $q_{\rm V}$ that we constrain using cosmic microwave background data from the Planck 2015 data release, along with baryon acoustic oscillation, redshift space distortion and Type Ia supernova measurements. We present the full linear perturbation theory of this interacting scenario and use MCMC sampling to study five different cases: two cases in which we have $Λ$CDM evolution in the distant past, until a set redshift $z_{\rm trans}$, below which the interaction switches on and $q_{\rm V}$ is the single sampled parameter, with $z_{\rm trans}$ fixed at $z_{\rm trans}=3000$ and $z_{\rm trans}=0.9$ respectively; a case where we allow this transition redshift to vary along with $q_{\rm V}$; a case in which the vacuum energy is zero for $z>z_{\rm trans}$ and then begins to grow once the interaction switches on; and the final case in which we bin $q_{\rm V}(z)$ in four redshift bins to investigate the possibility of a dynamical interaction, reconstructing the redshift evolution of the function using Gaussian processes. We find that, in all cases where the high redshift evolution is not modified, the results are compatible with a vanishing coupling, thus finding no significant deviation from $Λ$CDM.

astro-ph.CO↗